There are various forms of heating devices or heat exchange elements, comprising a pipe which contains an electrical resistance heating means or which carries a liquid or gaseous heat exchange agent, and a support member such as a panel or plate, to which or from which heat is passed or removed to produce the heat-emission or heat exchange function. It is necessary for the pipe structure to be secured to the support members such as a support plate or for example the bottom of a cooking or frying pan by a strong connection giving a long service life. In addition, however, it will be appreciated that the maximum level of heat transfer between the components is also of particular importance in order to arrive at a high degree of efficiency in the heat-emission or heat-transfer function. Both these conditions, namely a firm connection and a good heat transfer action, can be achieved by soldering or welding the pipe to the support plate. However, not only are soldering or welding operations of this kind expensive, but furthermore when the assembly comprises a pipe made by rolling a metal strip into a tubular form and welding or soldering the edges together, there is the danger that the resulting seam may come apart in the operation of welding or soldering the pipe to the support. Although this problem can be avoided by using seamless pipes, such pipes are too expensive for the more common uses of such assemblies.
In regard to electrical heating, cooking or frying equipment in which one or more tubular heaters are secured to a support panel for enhanced heat emission and radiation or to the vessel for receiving the items to be cooked or fried, there is also the difficulty that a not inconsiderable part of the heat produced by the heater is usually radiated from the side thereof which is remote from the support panel or vessel. Apart from the resulting loss of heat energy, there is a higher risk of fire if a heater burns through, particularly if the heater is disposed in a housing of plastic material. To reduce the heat losses, cover plates may be disposed around the heater but the production costs of such an assembly are substantially higher as the cover plates must in turn be secured to the support plates or to the bottom of the cooking vessel.